The present invention relates to an apparatus for making a thin unvulcanized rubber tape having a thickness in a range of from 0.3 to 1.5 mm.
Conventionally, unvulcanized rubber tires are made of unvulcanized rubber components having various shapes and sizes. As the unvulcanized rubber components are formed by extruders, the number and sizes of the extruders are depend on the maximum size and the number of the kinds of the rubber components. Usually, at least several extruders which are relatively large-sized are required.
In recent years, in order to decrease the number and size of extruders to decrease the plant size and to establish a flexible manufacturing system, it was proposed to make a pneumatic tire by winding an unvulcanized rubber tape G around a drum directly or indirectly thereon instead of applying a rubber component. For example, as shown in FIG. 7 which shows a tread rubber B having a trapezoidal cross sectional shape, a rubber tape G is overlap-wound across the width thereof. Therefore, on the surface of the formed rubber component B or the windings of the tape G, uneven part is formed due to the edges C of the windings of the tape G. Such unevenness of the surface can be prevented by using a very thin rubber tape having a thickness of 0.3 to 1.5 mm.
It is not difficult to decrease the thickness of unvulcanized rubber in itself. The thickness can be easily decreased by rolling, but due to the elasticity and adhesiveness, it is difficult to stably obtain a constant thickness without breakage. Further, it is also difficult to obtain a constant width. As a result an additional work to cut the edges of the rolled rubber tape into the predetermined width is necessitated.
It is therefore, an object of the present invention to provide an apparatus which can stably make an unvulcanized rubber tape with accuracy in width and thickness although the thickness is in a very small range of 0.3 to 1.5 mm.
According to the present invention an apparatus for making an unvulcanized rubber tape comprises
an extruder comprising a passage for unvulcanized rubber having an outlet for the extruded unvulcanized rubber, and
a pair of calender rollers disposed near the outlet for adjusting the thickness of the extruded unvulcanized rubber passing therebetween, wherein
the passage is made up of a transforming part having an inlet for the unvulcanized rubber at its upstream-side end, and a thinning part on the downstream side thereof defining the above-mentioned outlet at its downstream-side end,
the transforming part gradually changes in the cross sectional shape from a circle to a flat shape in the lower course of the passage,
the thinning part has a flat cross sectional shape and gradually decreases in the thickness in the lower course of the passage, and
a width W0 and a thickness T0 of the unvulcanized rubber tape, a width W1 of the inlet, a width WA and a thickness TA of the outlet, a length L of the transforming part, a width W2 of the transforming part at its downstream-side end, and a pressure P of the unvulcanized rubber flowing into the inlet satisfy the following relationships
0.7xc3x97W0xe2x89xa6WAxe2x89xa61.0xc3x97W0
1.5xc3x97T0xe2x89xa6TAxe2x89xa610xc3x97T0
WA less than W2 less than W1+0.2xc3x97L
P greater than 40 kgf/sq.cm.